This invention relates to a rotary fluid displacement apparatus, more particularly, to a fluid compressor unit or pump unit of the types which utilize an orbiting piston member.
There are several types of fluid displacement apparatus which utilize an orbiting piston or fluid displacing member driven by a Scotch yoke type shaft coupled to an end surface of the piston or member. One apparatus disclosed in U.S. Pat. No. 1,906,142 to John Ekelof, is a rotary machine provided with an annular and eccentricaly movable piston adapted to act within an annular cylinder with a radial transverse wall. One end of the wall of the cylinder is fixedly mounted and the other wall consists of a cover disc connected to the annular piston, which is driven by a crank shaft. Other prior art apparatus of this type are shown in U.S. Pat. No. 801,182 and 3,560,119.
Though the present invention applies to either type of fluid displacement apparatus, i.e., using either an annular piston or a scroll-type piston, the description will be limited to the scroll type compressor. The term piston is used generically to describe a movable member of any suitable configuration in fluid displacement apparatus.
U.S. Pat. No. 801,182 discloses a device including two scroll members each having an end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between spiral curved surfaces thereby to seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scroll members shifts the line contact along the spiral curved surfaces and, therefore, the fluid pockets change in volume. The volume of the fluid pockets increases or decreases dependant on the direction of the oribital motion. Therefore, the scroll-type apparatus is applicable to compress, expand or pump fluids.
Typically, a drive shaft receives and transmits a rotary driving force from an external power source. The drive shaft is rotatably supported by a bearing means disposed within a housing. In particular, as shown in U.S. Pat. No. 3,874,827, the drive shaft is rotatably supported by the two bearing means disposed within the housing.
Referring to FIG. 9, such shaft supporting constructions will be described. Adrive shaft 13' is formed with a disk portion 15' at its inner end portion and is rotatably supported by a first bearig means 19' disposed within a sleeve 17' projecting from a front end plate 11'. Disk portion 15' is also rotatably supported by a second bearing means 16' disposed within sleeve 17' of housing 10'. A crank pin of drive pin (not shown) axially projects from an end surface of disk portion 15', and is radially offset from the center of drive shaft 13'. The drive pin is connected to an orbiting scroll member for transmitting the orbital motion from the drive shaft 13' to the orbiting scroll member, and the orbiting scroll member is connected to a rotation preventing means, therefore orbiting scroll member is allowed to undergo the orbital motion by the rotation of drive shaft 13'.
In the above described shaft supporting construction, a load Fd, caused by a reaction force to the compression of fluid during the operation of the apparatus, acts on a bearing means 34' which rotatably supports the oribiting scroll member. Therefore, since drive shaft 13' is connected to the bushing 33' through the drive pin, this load Fd is transmitted to the shaft 13' which is rotatably supported by the two bearing means 16', 19' disposed within the sleeve 17' of front end plate 11'. At this time, the load FB.sub.1 and FB.sub.2 acting on the two bearing means 16' and 19' are given by:
FB.sub.1 =Fd+FB.sub.2, since the illustrated upwardly directed force is equal to the sum of the downwardly directed forces; and PA0 FB.sub.2 (X.sub.2)=Fd(X.sub.1), since these oppositely directed moments are equal.
Therefore, if the distance X.sub.2 is made longer, the load FB.sub.1 and FB.sub.2 acting on the two bearing means would be decreased and thereby the durability of these bearing means would be improved. However, in the general construction of the apparatus, a shaft seal assembly 20' is assembled on the drive shaft 13' within the sleeve 17' of front end plate 11' and placed outwardly of and against the bearing means. Therefore, if the distance X.sub.2 is made greater, the total length of apparatus will be increased.
A scroll-type fluid apparatus of this type is suited for use as a refrigerant compressor of an automobile air-conditioner. Generally, the compressor is coupled to a magnetic clutch for transmitting the output of the engine to the drive shaft of the compressor. The magnetic clutch comprises a pulley, magnetic coil, hub and armature plate. The pulley, which is usually rotated by the output of the engine, is rotatably supported by the sleeve through a bearing means disposed on the outer surface of the sleeve, and the magnetic coil is fixed on the outer surface of the sleeve.
The sleeve, which supports the pulley and magnetic coil, extends from an end surface of the housing and is cantilevered, therefore, the sleeve requires mechanical strength. Because tensile force of the belt which connects the pulley and the engine for transmitting the rotary motion is transmitted to the sleeve through the pulley and the bearing means, the thickness of the sleeve has a lower limit so that diameter of the bearing means which supports the pulley cannot be decreased. The outer diameter of compressor unit itself is thereby increased.